1. Field of the Invention
This invention relates generally to switching power supplies and, more particularly, to a pulse width modulator employing Schmidt trigger NAND gates.
2. Description of the Prior Art
Switching type power supplies are well known. A first type employs a fixed frequency oscillator wherein the output voltage is controlled by varying the pulse width. A second, less expensive type is one in which the on time in fixed and the output voltage is controlled by varying the off time. While the former is more accurate, it is both complex and expensive. The latter variety (fixed on time-variable off time) presents certain problems since as the load becomes smaller, the oscillator frequency decreases until eventually, the transformer output becomes audible. While not as expensive as the fixed frequency arrangements, this less expensive variety is still relatively complex.